Cycles does not render with GPU
Make sure, that you are running on newest drivers.

On linux run:
CYCLES_OPENCL_TEST=all ./blender

On windows:
set CYCLES_OPENCL_TEST=all
then run blender

Switch to cycles, go to system settings and select your graphic card.

The performance is limited and initial compiling of the kernel can take few minutes. But according to this AMD statement, there is a fix slowly coming in. No words on performance improvements though.